Life and Animus
The first thing one must keep in mind about the animus is that it is not the soul anymore than it is the body. It does not hold your memories, your hopes, your dreams, or your innermost self. It is instead the bridge by which that most ethereal self manipulates the physical form. It is the life force disrupted, manipulated, and even stolen by all manner of spells beginning with the First Circle. It is also the energy that makes up what are referred to as the 'Lesser Dead', not because they are not dangerous, a meeting with one of Wisdom Qyburn's works should put paid to that notion, but because they are not sapient, not ensouled.
Now all living things posses some manner of animus that can be sensed and utilized, even something as simple as a blade of grass. Does that then mean that said blade of grass could self-animate as an undead entity from a curse or great atrocity? No. Neither could say a clam or coral, not without intent from a necromancer to make them
more than simply a darkened reflection of what they were in life. The clam and blade of grass both lack motive will.
Some tomes, which I will not mention here so as not to give recognition to ignorance, claim that the distinction is the possession of a spine. This is mostly the conceit of mages who have not walked far enough afield into realms where vertebrates like you and I do not constitute the most common form of higher life, and indeed mages who have never stuck their heads beneath the water. Animating the common squid as one of the unliving is no more difficult than doing so to a rat.
Where the relationship between the animus and the divine matters become more murky, at least from the perspective of our limited material and time-bound selves, but some things can be concluded. Firstly, the animus itself, offered without ritual or care, without meaning, matters not at all. If one of you were to effortlessly collect a rat and hand it over to Yss to devour it would mean practically nothing, but if a starving beggar for which the rat might be the difference between life and death were to do the same, not only would the serpent god take greater note, He would gain quantitatively more power. Gods are stories in the end and stories do not feed upon merely abstract energy, they feed upon
meaning.
That is why the
Given sacrifice is more precious than that which is
Taken from the unwilling. But even here the distinction of what is being sacrificed matters. If one is say, sacrificing an existence one does not desire for a more pleasing rebirth,
that is worth far less than taking one's chances with the River of Souls and the judgement of one's god. Still, the mortal soul recoils from death, from the uncertainty of placing so much power into the hands of another, thus even that leap into the unknown might be made useful to the gods.
Ritual to Sacrifice the Animus of Undead will defray 40% of the cost of making a soul gem with Create Soul Gem (40 IM); Progress Required 20; 8,000 IM costs
One might rightly ask from the above question what is a ghost or spirit with the power of possession? Are they animus or soul? While spontaneously created spirits wrought of animus have been documented, they are rare and relatively fragile. Most of the incorporeal dead are exactly as they are commonly known, 'lost souls'. They overwhelm the victim of the possession and make use of their animus to control the victim. There is some indication that they also empower the bridge between body and soul in the process, the better to use their more esoteric powers, a fact which can lead to some long-term damage in the hosts.
Before anyone asks if the implications of the above would allow a specter to possess a beast so that the resulting stronger animus can be then offered up as sacrifice to the divine, the answer is yes. However, such a thing would require a willing wraith and quite a bit of study, so anyone intending to walk around with a mouse in their pocket to trap and sacrifice malicious ghosts will be sadly disappointed.
Ritual to allow the sacrifice of ghosts under above parameters requires Progress 30 and 14,000 IM
-Taken from the notes on the Restricted Mastery Class on soul magics
by Lya the Sage on the Fifth Day of the Second Month 294 after the Westerosi Reckoning
OOC: Ended up getting inspired to make this a full interlude.